A Wavelength Switched Optical Network (WSON) supports end-to-end optical paths, called lightpaths, between nodes requiring connection in the network. WSONs can be deployed across large areas and optical paths can be routed, if possible, with minimal electrical regeneration. Traffic is optically switched at intermediate nodes by Wavelength Selective Switches (WSS). Links in a WSON are operated in a Wavelength Division Multiplexed (WDM) manner, and carry traffic at a plurality of different wavelengths. When establishing a path between end nodes, the path may be assigned a particular wavelength for the entire end-to-end path between end nodes, or the path may be assigned different wavelengths on different legs of the path between end nodes if wavelength conversion is supported.
A Path Computation Element (PCE) has been defined as an entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. A Path Computation Client (PCC) is a client application requesting a path computation to be performed by the PCE. The PCC and PCE communicate through the PCE communication Protocol (PCEP). PCEP operations have been defined to enable effective PCE-based path computations and, in turn, the effective use of network resources. A PCE-based architecture is described in Internet Engineering Task Force (IETF) document RFC 4655 and the PCE communication Protocol is described in RFC 4657.
In a WSON, the Path Computation Client can be an end node which wishes to establish a path across the WSON. The PCE can be located anywhere within the network, and may be within an optical switching element, a Network Management System (NMS) or Operational Support System (OSS), or may be an independent network server.
Transponders in currently deployed nodes typically adopt unique, or statically configured, transmission technologies, e.g. a unique supported modulation format per transponder.
Specific PCEP operations have been defined for WSONs. They include, for example, the capability to enable impairment-validation and routing and wavelength assignment. US 2010/0220996A1 and “PCEP Extensions for WSON Routing and Wavelength Assignment”, draft-lee-pce-wson-rwa-ext-01.txt, March 2011, http://tools.ietf.org/html/draft-lee-pce-wson-rwa-ext-01 describe PCEP signalling in a WSON. These PCEP operations can send a transmission parameter such as a modulation format or a FEC type from a PCC to a PCE. These are simply used as inputs, or constraints, by the PCE and the PCE will attempt to calculate a path between the end nodes which meets the constraints.